/**
 * 合并二叉树
 * https://leetcode.cn/problems/merge-two-binary-trees/
 * 方法：深度优先搜索（递归）
 */
class  mergeTrees {
    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if(root1==null){
            return root2;
        }
        if(root2==null){
            return root1;
        }
        TreeNode root=new TreeNode(root1.val+root2.val);
        root.left=mergeTrees(root1.left,root2.left);
        root.right=mergeTrees(root1.right,root2.right);
        return root;
    }
}